Transversely-excited film bulk acoustic resonator with buried oxide strip acoustic confinement structures
Acoustic resonators, filters, and methods. An acoustic resonator includes a substrate, a piezoelectric plate, and a diaphragm including a portion of the piezoelectric plate spanning a cavity in a substrate. An interdigital transducer (IDT) on a front surface of the piezoelectric plate includes first and second sets of interleaved interdigital transducer (IDT) fingers extending from first and second busbars respectively. The interleaved IDT fingers extend onto the diaphragm. Overlapping portions of the interleaved IDT fingers define an aperture of the acoustic resonator. First and second dielectric strips are on the front surface of the piezoelectric plate. Each dielectric strip has a first portion under the IDT fingers in a respective margin of the aperture and a second portion extending into a gap between the respective margin and the respective busbar.
1. An acoustic resonator comprising:
a substrate;
a piezoelectric layer supported by the substrate and including a portion that forms a diaphragm that is over a cavity of the acoustic resonator;
an interdigital transducer (IDT) on the piezoelectric plate, the IDT comprising interleaved interdigital transducer (IDT) fingers extending from first and second busbars respectively, wherein:
the interleaved IDT fingers extend onto the diaphragm, and
overlapping portions of the interleaved IDT fingers define an aperture of the acoustic resonator;
a first dielectric strip on the piezoelectric layer, a first portion of the first dielectric strip under the interleaved IDT fingers in a first margin of the aperture and a second portion of the first dielectric strip extending into a first gap between the first margin and the first busbar; and
a second dielectric strip on the piezoelectric layer, a first portion of the second dielectric strip under the interleaved IDT fingers in a second margin of the aperture and a second portion of the second dielectric strip extending into a second gap between the second margin and the second busbar.
2. The acoustic resonator of claim 1 , wherein each of the first and second dielectric strips extend over an entire length of the IDT.
3. The acoustic resonator of claim 1 , wherein a thickness ts of each of the first and second dielectric strips and a thickness td of the diaphragm are related by:
0.008 td≤ts≤ 0.06 td.
4. The acoustic resonator of claim 1 , wherein a width dol of each of the first and second margins of the aperture and a thickness td of the diaphragm are related by:
0.6 td≤dol≤ 8.0 td.
5. The acoustic resonator of claim 1 , wherein a width ds of each of the first and second dielectric strips and a thickness td of the diaphragm are related by:
4.0 td≤ds≤ 16.0 td.
6. The acoustic resonator of claim 1 , wherein at least one of a width ds of each of the first and second dielectric strips, a width dol of each of the first and second margins of the aperture, and a thickness ts of one or both of the first and second dielectric strips varies along a length of the IDT.
7. The acoustic resonator of claim 1 , wherein the diaphragm further comprises an additional dielectric layer on and between the IDT fingers on the piezoelectric layer.
8. The acoustic resonator of claim 1 , wherein the piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT excites a primary shear acoustic mode in the piezoelectric layer.
9. The acoustic resonator of claim 8 , wherein the piezoelectric layer is one of Z-cut lithium niobate and Z-cut lithium tantalate.
10. A filter comprising:
a substrate;
a piezoelectric layer supported by the substrate and including a plurality of diaphragms that are over respective cavities of the filter;
a conductor pattern on the piezoelectric layer, the conductor pattern comprising interdigital transducers (IDTs) of a plurality of acoustic resonators, each IDT comprising interleaved interdigital transducer (IDT) fingers extending from first and second busbars respectively, wherein for each acoustic resonator of the plurality of acoustic resonators:
the interleaved IDT fingers extend onto a respective diaphragm of the plurality of diaphragms, and
overlapping portions of the interleaved IDT fingers define an aperture of the respective acoustic resonator;
wherein at least one acoustic resonator of the plurality of acoustic resonators further comprises:
a first dielectric strip on the piezoelectric layer, a first portion of the first dielectric strip under the interleaved IDT fingers in a first margin of the aperture and a second portion of the first dielectric strip extending into a first gap between the first margin and the first busbar; and
a second dielectric strip on the piezoelectric layer, a first portion of the second dielectric strip under the interleaved IDT fingers in a second margin of the aperture and a second portion of the second dielectric strip extending into a second gap between the second margin and the second busbar.
11. The filter of claim 10 , wherein each of the first and second dielectric strips extend over an entire length of the IDT of the at least one acoustic resonator.
12. The filter of claim 10 , wherein a thickness ts of each of the first and second dielectric strips and a thickness td of the diaphragm of the at least one acoustic resonator are related by:
0.008 td≤ts≤ 0.06 td.
13. The filter of claim 10 , wherein a width dol of each of the first and second margins of the aperture and a thickness td of the diaphragm of the at least one acoustic resonator are related by:
0.6 td≤dol≤ 8.0 td.
14. The filter of claim 10 , wherein a width ds of each of the first and second dielectric strips and a thickness td of the diaphragm of the at least one acoustic resonator are related by:
4.0 td≤ds≤ 16.0 td.
15. The filter of claim 10 , wherein at least one of a width ds of each of the first and second dielectric strips, a width dol of each of the first and second margins of the aperture, and a thickness ts of one or both of the first and second dielectric strips varies along a length of the IDT of the at least one acoustic resonator.
16. The filter of claim 10 , wherein the diaphragm of the at least one acoustic resonator further comprises an additional dielectric layer on and between the IDT fingers on the piezoelectric layer.
17. The filter of claim 10 , wherein the piezoelectric layer and the IDT of each of the plurality of acoustic resonators are configured such that a respective radio frequency signal applied to the respective IDT excites a respective primary shear acoustic mode in the piezoelectric layer.
18. The filter of claim 10 , wherein the piezoelectric layer is one of Z-cut lithium niobate and Z-cut lithium tantalate.
19. A method of fabricating an acoustic resonator, the method comprising:
forming an interdigital transducer (IDT) on a piezoelectric layer, the IDT comprising interleaved interdigital transducer (IDT) fingers extending from first and second busbars respectively, wherein:
the interleaved IDT fingers are on a diaphragm that is formed from a portion of the piezoelectric layer that is over a cavity in a substrate, and
overlapping portions of the interleaved IDT fingers define an aperture of the acoustic resonator; and
forming first and second dielectric strips on the piezoelectric layer, wherein:
a first portion of the first dielectric strip is under the interleaved IDT fingers in a first margin of the aperture and a second portion of the first dielectric strip extends into a first gap between the first margin and the first busbar, and
a first portion of the second dielectric strip is under the interleaved IDT fingers in a second margin of the aperture and a second portion of the second dielectric strip extends into a second gap between the second margin and the second busbar.